A resin composition comprising a propylene polymerization unit-containing resin and a nucleating agent is so superior in its property such as a mechanical property and transparency that it is widely utilized as a material for a use such as automobile interior parts, automobile exterior parts, home electric appliances, building materials, agricultural materials, convenience goods, films, bottles, caps, containers, and pallets.
Such a resin composition is disclosed in a patent document such as JP 2006-213918A (corresponding to US 2006-155073A) and JP 2009-508995A (corresponding to US 2007-66733A). The former document discloses a resin composition comprising a propylene-based block copolymer (A), which contains a propylene-based polymer component (I) and a component (II) obtained by copolymerizing propylene with a monomer selected from the group consisting of ethylene and an α-olefin having 4 to 12 carbon atoms, and a nucleating agent (B) having a particle diameter within a specified range. The latter document discloses a resin composition comprising a polyolefin and a nucleating or transparency agent dispersed or dissolved in the polyolefin.